The present invention relates generally to semiconductor device processing techniques, and, more particularly, to a method for reducing film stress for SiCOH low-k dielectric materials.
The continuous shrinking in dimensions of electronic devices utilized in ultra large scale integrated (ULSI) circuits in recent years has resulted in increasing the resistance of the back end of line (BEOL) metallization as well as increasing the capacitance of the intralayer and interlayer dielectric materials. This combined effect increases signal delays in ULSI electronic devices. In order to improve the switching performance of future ULSI circuits, low dielectric constant (low k) insulators (particularly those insulators with k values significantly lower than silicon oxide) are needed to reduce capacitances. One such commercially available, low-k dielectric material is polytetrafluoroethylene (“PTFE”), which has a k value of 2.0. However, this dielectric material is not thermally stable when exposed to temperatures above 300-350° C. Because dielectric materials used in ULSI chips need to have a thermal stability of at least 400° C., such dielectrics are rendered useless during integration.
Accordingly, some of the low k materials that have been considered for applications in ULSI devices include polymers containing elements of Si, C, O and H, such as, for example, methylsiloxane, methylsilsesquioxanes, and other organic and inorganic polymers. One problem with the use of such polymer low k films is that when the films are integrated in ULSI device processing, they exhibit poor mechanical properties such as, for example, a low elastic modulus, hardness, cohesive strength, as well as tensile stresses that result in cracking that is accelerated in the presence of water.
In view of the above drawbacks with prior art low-k and ultra low-k films, there remains a need for utilizing low-k, SiCOH dielectrics that have a desirable dielectric constant value (e.g., about 2.8 or less), but that also have improved mechanical properties such as reduced film stress.